Semiconductor chips are commonly provided in packages which facilitate handling of the chip during manufacture and during mounting of the chip on an external substrate such as a circuit board or other circuit panel. For example, many semiconductor chips are provided in packages suitable for surface mounting. These packages typically have an external structure with exposed terminals on a bottom face of the structure. The terminals are exposed at the bottom surface of the chip carrier. In the surface mounting operation, the package is placed onto a circuit board so that each terminal on the package is aligned with the corresponding contact pad on the circuit board. Solder or other bonding material is provided between the terminals and the contact pads. The package can be permanently bonded in place by heating the assembly so as to melt or “reflow” the solder or otherwise activate the bonding material. Numerous packages of this general type have been proposed for various applications. Most commonly, such packages include a dielectric element, commonly referred to as a “chip carrier” with terminals formed as plated or etched metallic structures on the dielectric. These terminals typically are connected to the contacts of the chip itself by features such as thin traces extending along the chip carrier itself and by fine leads or wires extending between the contacts of the chip and the terminals or traces. These packages also may include an overmolding or encapsulant covering the chip and also covering the upper of the chip carrier.
Chips used for generating or processing radio frequency (“RF”) signals, commonly referred to as “RF chips” are used in wireless devices such as cellular telephones and wireless data communication devices. There have been increasing needs for packages especially suited for use with RF chips with increasing adoption of wireless devices. RF chips typically generate substantial amounts of heat during operation. Moreover, RF chips require low impedance connections to external circuitry and in some cases require connections capable of handling appreciable electrical current. Moreover, packages for RF chips desirably incorporate electrical shielding which prevents unwanted propagation of electrical magnetic fields between the RF chip and the surroundings. For example, a radio frequency power amplifier chip used in a transmitter can generate significant spurious RF emissions. Other elements of the circuit must be protected from these emissions. Conversely, a radio frequency amplifier used in a receiver should be isolated from RF emissions generated by other components.
It is desirable to package RF chips in a unit containing other components such as, for example, inductors, couplers, chokes, capacitors and resistors separate from the RF chip itself. The entire package should be as small as possible to facilitate miniaturization of the overall wireless device. Also, such packages should be manufacturable at low cost and with high reliability. All of these factors, taken together, have presented a considerable challenge heretofore.